Square and rectangular ducting are widely used in HVAC systems. Such ducting can be located between floor or ceiling joists whereas ducting of other cross-sectional shapes, such as round, may not fit in such locations and still be sufficiently large enough in size to handle the HVAC load required.
Referring to FIGS. 1–3, it is known to manufacture square and rectangular single wall ducting structures such as structure 20, by bending a sheet of thin-gauge material to form the corners and the four walls of a length of ducting 22 and then join the duct together along one corner 24 to form an integral structure. This corner joint may take various forms, such as by overlapping portions of the ducting and then screwing the overlapped portions together, or by utilizing an “S” shaped flange 26 or other shaped member to join the ducting along corner 24. Typically, lengths of square and rectangular ducting produced in this manner are relatively limited in length due to the size of the brake press or other machinery used to form the corners of the ducting and also limited by the length of the sheet metal stock available.
Because square and rectangular cross-section HVAC ducting is typically of relatively short lengths, it is necessary to connect ducting sections end-to-end to achieve a desired overall length. In this regard, as shown most clearly in FIGS. 1 and 2, a face flange structure 28 is integrally formed at the ends of each wall of the duct 22. The face flange structure has a mating or face section 30 extending perpendicularly to the corresponding wall of duct 22 and a reinforcement hem structure 32 extending transversely from the distal edge flange face 30. The hem structure 32 may be folded over on itself to form a double thick section for additional strength. In FIG. 1, the hem structure 32 is folded inwardly on itself whereas in FIG. 2, the hem section is folded outwardly on itself.
As will be appreciated by the foregoing construction, it is not possible to extend the face flanges 28 to occupy the entire corner at the juncture between two adjacent panels of the ducting structure 20. Such open corners are “filled in” by an angle bracket 34 that typically nests with the adjacent portions of the face flange structures 28. FIG. 1 shows the angle brackets 34 prior to installation, whereas FIG. 2 illustrates the angle flanges in installed positions. The angle flanges include corner apertures 35 for receiving a hardware fastener 36 therethrough. The hardware fastener may be in the form of a threaded screw that mates with a nut 38. In this manner, the face flange structures 28 are connected together in face-to-face relationship at the corners of the ducting structure 20. A flat or other shaped gasket 40 may be interposed between adjacent flange faces 30 in an effort to provide an airtight seal therebetween.
However, a sufficient seal usually is not achieved through the use of only the angle brackets 34. As such, typically formed clips 40 are used to also retain the adjacent face flange structures 28 together in an engaged face-to-face relationship. As shown in FIG. 2, the clip 40 is shaped and sized to wrap around the reinforcement hem structures 32 of the face flange structures 28.
Referring to FIG. 3, typically reinforcing members are needed to increase the structural integrity of ducting sections 20 and to prevent the ducting sections from unduly vibrating. FIG. 3 illustrates such reinforcing members in the form of “Z” brackets 42 that extend transversely across duct 22, with one of the flange sections of the brackets attached to the duct by hardware members, welding or otherwise.
It can be appreciated that the prior art single wall ducting structure shown in FIGS. 1–3 is time-consuming and expensive not only to fabricate, but also to assemble and install in the field. The present invention is directed to economical and rapid methods for manufacturing, assembling and installing HVAC double wall ducting of a rectangular or square cross-section.